The invention relates to a power supply particularly to a power supply for supplying power to a load of a portable equipment using a battery.
Various portable equipment such as a cellular phone, a portable computer, a portable tape recorder, a portable CD player, and an electronic notepad have been used, and there are desired a battery which is small and light and is capable of supplying power for a long time, and a power supply using the same.
An example of conventional portable equipment which is built in such a power supply is shortly described with reference to FIG. 6. According to the portable equipment, power is supplied to a load 60 by a power supply consisting a battery 10 and a power supply circuit 15 which is serially connected with the battery 10.
A load 60 comprises a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, an LCD (Liquid Crystal Display) 63, an input device 64 such as a keyboard or the like, a RAM (Random Access Memory) 66 and an RTC (Real Time Clock) 67.
There are three types of operation modes of the load 60, namely, a so-called full mode or normal mode where all the CPU 61, ROM 62, LCD 63, input device 64, RAM 66, and RTC 67 operate, a so-called idle mode or sleep mode where a part of the CPU 61 and the LCD 63, RAM 66 and RTC 67 operate, and a so-called stop mode where only the RAM 66 and RTC 67 operate.
There is a difference between the current consumption in the full mode where all the components of the load operate and the current consumption in the stop mode where only the RAM 66 and RTC 67 operate in the order of several hundreds to several thousands.
For example, current consumption of a certain model of a card type PDA (Personal Digital Assistant) manufactured by Citizen Watch Co., LTD. is 10 mA in the full mode, while it is several tens xcexcA in the stop mode.
A power supply circuit type is generally classified into a switching regulator circuit type and a linear regulator circuit type. A power supply circuit of the portable equipment generally employs the switching regulator circuit type so as to extend the battery life, so that the maximum power conversion efficiency is obtained in the full mode where all the components of the load operate or in the idle mode of a standby state. However, in a state such as the stop mode where the load is very small, the linear regulator circuit type which does not use an oscillator for pulse width modulation is small in quiescent current of the power supply circuit per se, thereby enhancing power conversion efficiency.
The power supply circuit 15 in FIG. 6 converts an input voltage and input current from the battery 10 into an output voltage and output current suitable for the load 60 and supplies to the same. The power supply circuit 15 of the conventional portable equipment employs the power supply circuit of the switching regulator circuit type so as to supply power to the load 60 so that the maximum power conversion efficiency is obtained in the full mode operating all the components of the load 60 or the idle mode.
However, the quiescent current of the switching regulator circuit type power supply circuit is several tens to several hundreds times as large as that of the linear regulator circuit type power supply circuit. Therefore, the current consumption of the power supply circuit per se becomes larger than current consumption of the load during the stop mode, so that it is not always sure that power conversion efficiency is the maximum in all operation modes.
The invention has been developed to solve the foregoing problems, and it is an object of the invention to provide a power supply capable of reducing current consumption of a power supply circuit per se during a stop mode to enhance power conversion efficiency, thereby obtaining the maximum power conversion efficiency in all operation modes.
To achieve the above object, a power supply of the invention comprising, a power supply circuit connected with the battery for supplying power to a load, wherein the power supply circuit consists of a plurality of power supply circuits which are connected in parallel with one another.
The power supply unit further comprises an operation mode detecting means for detecting an operation mode of the load, and a power supply circuit selecting means for switching any one of or multiple combinations of the plurality of power supply circuits for supplying power to the load depending on the operation mode detected by the operation mode detecting means.
The load is provided with a CPU, and the operation mode detecting means consists of the CPU per se, or a detecting means for the operation mode of the load in response to a signal representing the operation state of the CPU.
It is preferable that the plurality of power supply circuits mentioned above are differentiated in a circuit type or power supply characteristics. For example, it is preferable that the plurality of power supply circuits comprise a first power supply circuit which is a switching regulator circuit type and a second power supply circuit which is a linear regulator circuit type, and when the operation mode of the load is a full mode or an idle mode, power is supplied to the load by the first and second power supply circuits, while the operation mode is a stop mode, power is supplied to the load by the second power supply circuit alone.
According to the power supply of the invention having the foregoing construction, it is possible to supply power to the load by selecting the power supply circuit or the combination of the plurality of the power supply circuits either of which obtain the maximum power conversion efficiency depending on the operation mode of the load. Accordingly, it is possible to improve power conversion efficiency in the all operation modes, for example, by reducing current consumption of the power supply circuit per se during a stop mode.